1. Field of the Invention
This invention relates generally to the field of control circuits for electronic equipment. More particularly, this invention relates to a controller which permits a single switch to perform a plurality of transceiver functions which may be dependent upon the status of the receiver or the transmitter, or the recent actuation history of the switch itself.
2. Background of the Invention
As the state of the art in the electronic industry progresses, the trend is towards ever smaller electronic devices which must reliably perform a variety of functions. An example of this trend may be found in the field of electronic calculators. While the predecessor of the modern pocket calculator literally occupied rooms, devices with similar computational power which will fit in a shirt pocket are now commonplace. Such devices often have control buttons which electronically address a number of different features per button in order to provide the user with a large number of features in a small package. This is accomplished by using a "second feature button" which is actuated prior to the actuation of a button which addresses a plurality of features. Therefore, in order for the user to address the features of his calculator, two button actuations are required to address a single feature.
In the field of portable radio transceivers, there is a similar size reduction trend taking place. As the size of these devices diminishes, the number of control features incorporated in a single control switch must also increase in order for the user to control the additional electronic features incorporated therein.
This is particularly true for selective calling portable radio transceivers (radio transmitter/receivers) such as those commonly used throughout Europe. In these systems the user is required by regulation to monitor his receiver prior to making any transmission to assure that there is no channel activity taking place on the communication channel he intends to use. Once the user establishes that the channel is free of activity, he must normally transmit a series of tones or a digitally encoded message in order to address the receiver or repeater he desires to contact. For example, in the well known ZVEI (Zentral Verband der Elektro-Industrie) system commonly used in Germany, an address code consists of a sequence of five audio frequency tones between 1060 Hz and 2600 Hz which are consecutively transmitted. Each tone has a 70 millisecond duration with no pause between tones. Each tone represents a single digit 0-9 (or a repeat tone indicating that the preceeding digit is repeated). Each user or repeater is assigned a five digit address which must be correctly decoded to access that receiver or repeater. Encoding and decoding circuits for such systems are well known. Having established receiver or repeater access, the user is then free to carry on normal two way voice or data communications with another transceiver.
One scheme often used to accomplish the above sequence of steps is to provide the portable transceiver with three switches. In operation, the user firsts actuates a "push-to-monitor" switch which enables the receiver section audio so that the user may determine if there is activity taking place on the desired radio frequency channel. When the channel is clear, the user actuates a second switch which transmits an appropriate code word in tones or binary digits, as for example, a set of five sequential tones of predetermined length and frequency, to access the desired receiver. The user then actuates a third switch to enable his transmitter and microphone in order to carry on normal conversation.
In the above transceiver scheme, a total of three switches are required to perform even the most basic selective calling transceiver functions. In addition to these controls, the transceiver must also include a volume control, an on/off switch, a squelch control, a channel selector control, and quite possibly many other controls such as a telephone style keypad for more sophisticated transceivers. It is evident that utilizing three separate switches simply to control the sequence of steps necessary for initialization of a conversation is highly inefficient. As these transceivers incorporate more and more features and options, the switch requirement becomes a severe size limitation in a portable or mobile transceiver.
Another scheme often used in portable transceivers, such as Motorola's European version of its MX300 series of transceivers, utilizes a momentary push-to-talk type switch in conjunction with a three position toggle switch. This exemplifies the utilization of a two switch requirement for the selection of any transceiver function. In this scheme a first position of the toggle switch places the radio receiver in a coded squelch mode. This makes the radio reciever responsive only to tone or digitally encoded messages bearing an appropriate user address code. The center position of the toggle switch places the receiver in the carrier squelch mode which allows the receiver to turn on its audio amplifier and speaker upon receipt of any message on the communication channel without regard to coding. The third position of the toggle switch enables the transmitter and transmits the encoded message required to access a receiver or repeater.
In operation, if the user wishes to initiate a call he switches the toggle switch from the coded squelch position to carrier squelch position in order to monitor the channel for activity by other users. He then moves the toggle switch to the encode mode to transmit an appropriate address code to access an appropriate receiver. The user may then utilizes his "push-to-talk" (PTT) switch in a normal manner as necessary to carry on the desired conversation. This system has the advantage of forcing the user to monitor the channel prior to transmitting the code to access a receiver since he has to pass through the carrier squelch position of the three position switch in order to initiate a call. After completing the conversation, the user must switch his transceiver back to the coded squelch mode.
Another two switch system is used in radios such as the GRUNDIG MODEL FK103. In this system a first switch turns ON the receiver audio so that the user may monitor the channel. Deactuation of the switch places the transceiver in a coded squelch mode. Actuation of the second switch while in the coded squelch mode reverts the receiver to carrier squelch and transmits the address code. All subsequent transmissions are without encoding and the first switch is actuated again to place the radio back in the coded squelch mode.
Although these systems reduce the number of switches required to two, operation of the transceiver with one hand can be quite awkward. They inefficiently utilize valuable transceiver controls to actuate only basic transceiver functions not to mention increasing their cost. Also, the user is required in each case to manually place the transceiver back in a coded squelch mode after conversation has ended.